In-liquid Plasma Catalysis for Nitrogen Reduction

TL;DR

This paper presents a novel in-liquid plasma catalysis method combining plasma activation and electrocatalysis for ammonia synthesis from nitrogen, achieving high partial current densities without added hydrogen.

Contribution

It introduces a dual plasma-electrocatalysis system utilizing platinum, demonstrating enhanced ammonia production beyond traditional methods and eliminating the need for external hydrogen sources.

Findings

Platinum is the most stable and active catalyst tested.

Achieved partial current densities up to 3 mmol h-1 cm-2 at 250 mA cm-2.

Synergistic effect confirmed across various metals.

Abstract

Ammonia, a crucial component in fertilizers and fuels, is currently produced by the energy-intensive Haber-Bosch process. However, due to the high upfront investments required for large-scale centralized production, alternative routes for small-scale applications are being sought. We integrate in-liquid plasma with electrocatalysis for ammonia generation via the nitrogen reduction reaction (NRR). Among materials tested, platinum emerged as the most stable and active catalyst - it evolves hydrogen without plasma but produces significant ammonia under cold or hot in-liquid plasma. Our system employs a dual mechanism: plasma activates N2, while the elevated Pt electrode temperature drives water decomposition (thermally and via plasma pathways), releasing reactive hydrogen. This synergy stabilizes key NH intermediates, enabling ammonia production beyond conventional electrocatalysis and eliminating the need for added hydrogen. Under optimized plasma conditions, partial current densities up to 3 mmol h-1 cm-2 at 250 mA cm-2 are achieved. Control measurements across various metals confirm a synergistic plasma-catalysis effect.